Desiccant composition

ABSTRACT

Disclosed is a new desiccant composition containing calcium chloride and starch. Preferably the starch is a modified starch, preferably a modified corn starch. The composition contains from about 5 to about 95 percent calcium chloride and from about 5 to about 95 percent starch.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of Ser. No. 08/715,067, filed on Sep. 19,1996 now U.S. Pat. No. 5,743,942.

BACKGROUND OF INVENTION

1. Field of Invention

This invention relates to desiccant containers. More specifically, thisinvention relates to a composition of material for use in a desiccantcontainer comprising a combination of calcium chloride and starch.

2. Prior Art

Desiccant containers which absorb water vapor, water, liquids and thelike are well known in the art. Generally, these containers arecomprised of a water or water vapor permeable packaging material formedfrom fibrous or film products securely sealed together at the edges ofthe packaging. The packaging material encapsulates a desiccant material,such as silica gel. The volume of water or water vapor absorbed by thedesiccant container is generally determined by the absorbent capacity ofthe desiccant material contained within the container.

One type of desiccant container absorbs both water vapor and liquidwater by permitting both to pass through the packaging material to beabsorbed by the desiccant material. In some circumstances, the packagingmaterial for this type of product dissolves to permit the desiccantmaterial contained within the desiccant container to have direct contactwith the liquid.

Another type of desiccant container absorbs water vapor but not liquidwater. The packaging material for this type of desiccant container isdesigned to prevent water absorbed within the desiccant container aswater vapor from being released from the desiccant container in the formof liquid water.

There are many common products that are utilized as desiccating agents.Among the most common used include silica gel, calcium sulfate, calciumfluoride, activated charcoal, molecular sieves, lithium chloride,calcium chloride and other such products. A common list of these dryingagents is contained, for example, in Kirk-Othmer, Encyclopedia ofChemical Technology, Volume 7, pages 378-398. Common desiccating agentsfor use in conventional desiccant containers are also disclosed in U.S.Pat. No. 5,114,003, which discloses the use of a montmorillonite clay,silica gel, molecular sieve, calcium oxide, calcium sulfate and calciumchloride. The use of silica gel, alumino silicate, alumina, activatedcharcoal and molecular sieves as desiccating agents are disclosed inU.S. Pat. No. 4,464,261.

Commercial grade calcium chloride is a widely used desiccant due to itslow cost and high degree of hygroscopicity. Calcium chloride compactedin the form of particles or beads is used as a drying agent, forexample, in U.S. Pat. No. 3,923,944.

Mixtures and combinations of other materials have been combined withcalcium chloride to form desiccating products. For example, polyethyleneglycol was mixed with calcium chloride to form a desiccant product inU.S. Pat. No. 3,779,936. In addition, U.S. Pat. No. 3,334,468 disclosesthe use of sodium chloride or sodium carbonate with calcium chloride.Further, the combination of calcium chloride with magnesium, lithium orammonium salts is disclosed, for example, in U.S. Pat. No. 3,885,926.The use of calcium chloride with a metal, for example, iron fillings, isdisclosed in U.S. Pat. No. 1,798,862. Further, the use of activatedcarbon with calcium chloride as a desiccant product is disclosed in U.S.Pat. No. 2,027,093.

U.S. Pat. No. 3,390,511 discloses the use of calcium chloride placed ona carrier material for use as a gas dryer desiccant. The preferredmaterial that is utilized as the carrier for the calcium chloride issodium chloride. See also, U.S. Pat. No. 3,334,468. The desiccantproduct in U.S. Pat. No. 3,390,511 preferably comprised about 90 to 97percent sodium chloride as the carrier and about 10 to about 3 percentcalcium chloride. In addition, sodium dichromate and trisodium phosphatein minor amounts may be included in the product. While the preferredcarrier for the calcium chloride was sodium chloride, other disclosedcarriers included sugar, potassium chloride, potassium nitrate, sodiumnitrate and starch. See column 3, line 33. The percentage of calciumchloride used in this product was 10 percent or less, because the majorcomponent of the product was the carrier.

One of the problems in the utilization of calcium chloride as adesiccating agent is that when the water is absorbed, it forms a liquidmixture on the surface of the calcium chloride. This is discussed inU.S. Pat. No. 3,334,468. With conventional desiccant products thisliquid may leak which can cause problems, for example, if the desiccantproduct is used in storage containers.

While these references disclose the use of calcium chloride as adesiccant either alone or combined with a number of differentcompositions, there is still the need for improved desiccant productsutilizing calcium chloride.

Therefore it is an object of this invention to disclose a desiccantcomposition containing calcium chloride as its major component.

It is a still further object of this invention to disclose a desiccantcomposition containing calcium chloride mixed with a significant amountof starch to form the desiccant composition.

It is a still further object of the invention to disclose a desiccantcomposition contained within a packaging material, wherein the desiccantcomposition is a combination of calcium chloride and starch, preferablya modified starch.

It is a still further object of this invention to disclose a desiccantcomposition containing calcium chloride where water absorbed by thecalcium chloride does not leak from the desiccant container.

It is a still further object of this invention to disclose a desiccantcomposition contained within a packaging material wherein the desiccantcomposition prevents leakage of water from within the package by use ofa starch, preferably a modified starch.

These and other objects and features of the present invention willbecome apparent to those skilled in the art from a consideration of thefollowing detailed description, drawings and claims. The description,along with the accompanying drawings, provides a selected example of theconstruction of the product and process to illustrate the invention.

SUMMARY OF INVENTION

In accordance with the present invention there is provided a desiccantcomposition comprising calcium chloride and starch, wherein the calciumchloride comprises at least about 5 to about 95 percent of thecomposition by weight and the starch from about 5 to about 95 percent ofcomposition. In the preferred embodiment calcium chloride comprises fromabout 20 to about 95 percent of the composition by weight while thestarch comprises from about 5 to about 80 percent of the composition byweight. While the starch used may be unmodified, in a preferredembodiment, it is a modified starch, preferably a modified corn starch.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will now be described with reference to the accompanyingdrawings in which:

FIG. 1 is a perspective view of the desiccant container.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Although the invention is adaptable to a wide variety of uses, it isshown in the drawings for the purpose of illustration as embodied in adesiccant container (10) for absorbing and immobilizing a liquidcomprised of a desiccant packaging material (12) encapsulating a liquidabsorbing and immobilizing desiccant material (14). See FIG. 1.

The desiccant packaging material (12) may comprise any conventionalpackaging material. Preferably, it comprises a laminated film layer (16)with an inner (18) and outer (20) surface preferably formed from anuncoated microporous or nonwoven film layer sealed to an uncoated, watervapor permeable laminate film (22) with an inner (24) and outer (26)surface. The inner surface of the layers are sealed at the edges asshown in FIG. 1.

Conventional microporous or nonwoven films used for the manufacture of alaminated packaging material have been formed into a composite filmbonded to another layer of material. Conventionally, the bonding of thetwo layers is accomplished by the use of an adhesive which coats one orboth of the inside surfaces of the layers. It has been surprisinglydiscovered that strong, laminated desiccant packaging materials can beproduced from uncoated microporous or nonwoven films.

The uncoated microporous or nonwoven film (16) comprises a film having aplurality of fine openings, which film is gas permeable, but waterimpermeable when there is no difference between the air pressure outsideof the film and inside of the film. The size of the openings ispreferably in the range of about 0.01 to 50 microns. The uncoatedmicroporous or nonwoven film may constitute a single film layer or maycomprise a laminate of separate microporous film layers. Preferably thefilm is a single layer microporous film formed from a polyolefinicmaterial, such as polyethylene, polypropylene, poly(fluorinatedethylene), ethylene vinyl acetate, ethylene acrylic ester and the like.The uncoated microporous or nonwoven film may be prepared by anyconventional film forming process including cold orientation of thefilm, orientation of different substance-containing films, extraction ofdifferent substances from different substance-containing films,extraction of different substance-containing film followed byorientation of the treated film, cross-dispersing of a bundle of fibersfollowed by heat-pressing the resulting film and any other conventionalprocedures utilized for the formation of a microporous film. Many suchmicroporous films are commercially available and are sold, for example,under the name Celgards (Hoechst Celanese Corporation), GORE-TEX® (Gore& Co. Gmbh) and Tyvek® (E.I. DuPont). The preferred microporous film hasa Gurley-type air permeability of about 0.01 to 10,000 sec./100millimeters, preferably 1 to 1,000 second/100 millimeters and mostpreferably less than about 400 seconds/100 millimeters. Preferably, themicroporous film is a polyethylene or polypropylene-based microporousfilm and most preferably a polyethylene spun-bonded paper such as Tyvek®1059B or 1037B manufactured by E.I. DuPont, or a polypropylene basedfilm, such as GDT II manufactured by San Ai, Ltd. of Osaka, Japan.

The second layer of the desiccant packaging material is preferablyformed from the uncoated laminate film (22). The laminate film can beformed of conventional polymeric materials. The critical aspect of thecomposition of the laminate film is that its inner surface (24), whichis bonded to the inner surface (18) of the uncoated microporous ornonwoven film layer at the edges of the packaging material, must becomprised of materials which are compatible with the composition of theinner surface of the microporous or nonwoven film layer. Materials thatcan be used to form this laminate film include conventional polyolefinicmaterials such as polyolefinic polypropylene, polyolefinic polyethylene,polyesters and the like. Preferably, the uncoated laminate film has alower moisture vapor transmission rate than the microporous or nonwovenfilm. Also preferably the softening temperature of the uncoated laminatefilm is lower than or equal to the softening temperature of the innersurface of the uncoated microporous film. Preferably the laminate filmis comprised of a laminated film comprising a high melting or softeningpoint material, such as polyester, located on one side laminated to alower melting point material, such as polypropylene on the oppositeside. Examples of acceptable laminate film include, for example,RPP91-1964 or RPP-31-1007a manufactured by RollPrint.

The outer surface (26) of the laminate film are preferably formed frommaterials which are incompatible with the microporous layer, such asmaterials having a higher melting or softening point than that of theinner surface of the microporous film, such as polyester material. Incontrast, the inner surface of the laminate film (24) must be formedfrom a material which is compatible with the inner surface (18) of themicroporous film. By having the two inner surfaces formed fromcompatible materials, a strong bond is formed between those layers whenthey are heat sealed together.

"Compatible" means that the materials mix on a molecular scale and willcrystallize homogeneously. Thus, while such layers may not haveprecisely the same softening point, they should have softening pointswhich are consistent, so that the materials will mix on a molecularlevel. Compatible bonds generally have a bond strength of at least about5 lb./in. or more. For example, the compatible materials may includehigh density, low density, or linear low-density polyethylenes as wellas nonoriented, bi-axially oriented or laminated polypropylenes. Incontrast, the outer surface of at least the laminate film should bemanufactured from incompatible materials such as polyester or nylon or apolyethylene or polypropylene material with a higher softening pointthan the inner surface of the laminate film material.

In addition, it is also critical that the inner surface of both thelaminate film and the microporous or nonwoven film be uncoated with anadhesive. Coated film, when sealed to other coated or uncoated films,frequently form poor quality, weak seals. In addition, the sealingmachines used for sealing coated films are also more expensive and moredifficult to operate, resulting in greater expense for the manufactureof sealing coated films. Further, uncoated films are generally lessexpensive than coated films, sometimes by as much as 50 percent.

Suitable materials for use as the desiccant material to be incorporatedinto the desiccant package include conventional desiccating materialsuch as silica gel, clays, calcium chloride, alkali metal carboxylatesalts of starch--polyacrylonitrile, sodium polyacrylate and otherdesiccating products that absorb, gel or thicken upon contact with wateror water vapor. However, it has been surprisingly discovered that apreferred desiccant material can be produced from a mixture of calciumchloride and starch, preferably a modified starch, and most preferably amodified corn starch, such as MIRA-SPERSE® 623, 626 and 629 produced byA.E. Staley Manufacturing Company. The composition of this desiccantmaterial is preferably about 5 to about 95 percent calcium chloridemixed with about 95 to about 5 percent starch. Preferably, the calciumchloride comprises about 20 to about 95 percent while the starchcomprises about 80 to about 5 percent of the composition. Mostpreferably the calcium chloride comprises about 50 to about 80 percentwhile the starch comprises about 50 to about 20 percent of thecomposition.

The starches that are utilized in this invention can include unmodifiedstarches, oxidized starch, enzyme-converted starches and modifiedstarches containing functional groups such as hydroxyl, carbonyl, amidoand amino groups. The term "starch" therefore as used throughout thisspecification and claims is intended to include any member of the familyof starches, or mixture of two or more starches. The preferred starch isa modified starch, such as an oxidized, enzyme-converted starch. Themodification to the starch may be chemical, such as by crosslinking orsubstitution, or physical, such as by granulation.

Ordinary starch, such as pearl starch, is not commonly utilized in itsraw state because of its high viscosity and retrogradation, which is aparticular problem with unmodified starches. These problems are reducedsubstantially with modified starches, such as hydroxyethylated starches.As such, most industries convert their unmodified starches to modifiedstarches, such as oxidized, enzyme converted or hydroxyethylated starch.Alternatively, a further modified starch, in the form of a cationicstarch, can be used. However, the cost of such cationic starch issignificant in comparison to either unmodified or hydroxyethylatedstarch. Critical to the choice of starch is its ability to absorb water,preferably cool water, i.e., less than about 40-50° C.

In a preferred embodiment the starch when combined with water must havea viscosity greater than water alone. When measured as Brookfieldviscosity, the viscosity should be at least about 1.0 cps. The criticalfunction supplied by the modified starch is the ability to mix withwater and thicken or gel water or the calcium chloride/water compositionformed during the absorption of water by calcium chloride.

The calcium chloride/corn starch desiccant composition can be used notonly with the desiccant container outlined above, but also with anyconventional desiccant container utilized for the absorption of water orwater vapor.

The process for the formation of the desiccating container comprises anumber of steps. The desiccant packaging material is first formed. Toform the desiccant packaging material of the instant invention, theuncoated microporous and nonwoven film (16) is first formed or acquiredfrom conventional sources. In a preferred embodiment the microporousfilm is an uncoated microporous or non-woven film such as Celgard®produced by Hoechst Celanese Corporation, Tyvek® Nos. 1059B and 1073Bproduced by E.I. DuPont or certain other polypropylene-based non-wovenfilms such as GDTI, II produced by San Ai of Osaka, Japan. As statedabove, the permeability of this microporous film should be in the rangeof about 1 to about 1,000 Gurley seconds per 100 millimeters andpreferably less than about 400 seconds per 100 millimeters.

Following the formation of the uncoated microporous or nonwoven film,the uncoated laminate film (22) is formed. As stated above, thisuncoated laminate film can be comprised of different layers of the sameor different materials laminated together. However, the critical elementof the composition of this material is that the film must be uncoatedand the inner surface (24) of the laminate film, which is sealed to aninner surface (18) of the microporous material, must be formed of amaterial which is "compatible" with the inner surface of the uncoatedmicroporous or nonwoven film. In one preferred embodiment, the laminatefilm is a laminated film containing a polyester material on the outersurface with a polypropylene material on the inner surface, such as RPP91-1964 made by RollPrint. Another preferred embodiment is RPP 31-1007A,a polyethylene-based material also manufactured by RollPrint.

Following the formation of the two layers, the edges of the layers aresealed together by a conventional heat sealing procedure. One of theadvantages of this product is that the bond formed between the twocompatible, uncoated materials has a significantly greater strength thanconventional bonds utilizing an adhesive coating. By utilizing thecapability of compatible materials to form a strong seal without usingan adhesive, the strength of the desiccant packaging material issignificantly increased over conventional packaging materials. Inaddition, these uncoated materials have a lower cost of production andrun better through the sealing equipment.

The preferred desiccant material is then placed within the desiccantpackaging. By using the preferred desiccant material (14) formed fromcalcium chloride and starch, preferably a modified starch, lesserquantities of the desiccating material may be necessary than is used inconventional desiccating containers and still achieve the same level ofmoisture absorbency.

The mixture of the calcium chloride and starch is prepared by placingthe two components in a conventional mixing apparatus, such as tumblemixer or the two components can be fed directly into the desiccantpackaging from two separate feeds. Other than the physical mixing of thematerials, no additional processing is necessary for the calciumchloride/starch composition. This simple mixing of the two materialsproduces a desiccant composition with great utility.

Following the addition of the desiccant material to the desiccantpackaging material, the remaining unsealed edges of the desiccantcontainer are sealed to complete the formation of the desiccantcontainer.

EXAMPLES Example 1

The water absorbing capability of a desiccant combination comprisingcorn starch with calcium chloride was tested. 133 grams of a 3 to 1mixture of calcium chloride to Mirasperse 629 modified waxy corn starchsold by Staley Food Ingredients, Decatur, Ill. was placed in aconventional desiccant bag for a desiccant product, which product issold by United Desiccants and known as "CONTAINER DRI®". The desiccantbag was placed in environmental chamber of 80 percent relative humidityat 25° C. for about two months.

Example 2

The same tests were run on a composition of 1 to 4 corn starch tocalcium chloride utilizing the same type of Mirasperse 624 modified cornstarch as was discussed in Example 1.

Example 3

The water absorbance of a conventional 500 gram CONTAINER DRI® desiccantproduct produced by United Desiccants was compared with the products ofExamples 1 and 2 using the same procedures as were used in Example 1.

In addition, the capacity of a 1:4 ratio modified starch/calciumchloride product of Example 2 was compared with the conventional 500gram CONTAINER DRI® product.

As is clear from these examples, greater water absorption is shown for acomposition of corn starch and calcium chloride in comparison with theconventional desiccant material. This water absorption capability is atleast as good as conventional desiccant packages conventionally sold. Inaddition, the desiccating composition of Example 2 was compared with theCONTAINER DRI® product after 265 hours. Because of the capability of thestarch to absorb the water and the liquid calcium chloride on thesurface of the calcium chloride product, water did not leak from thecontainer even after three months.

We claim:
 1. A desiccant composition calcium chloride and a modifiedstarch, wherein the calcium chloride comprises at least about 5 to about95 percent of the composition by weight and the modified starch fromabout 5 to about 95 percent of the composition.
 2. The desiccantcomposition of claim 1 wherein the calcium chloride comprises from about20 to about 95 percent of the composition by weight and the modifiedstarch from about 5 to about 80 percent of the composition by weight. 3.The desiccant composition of claim 1 wherein the calcium chloridecomprises from about 50 to about 80 percent of the composition by weightand the modified starch from about 20 to about 50 percent of thecomposition by weight.
 4. The desiccant composition of claim 1 whereinthe starch is a modified corn starch.
 5. The desiccant composition ofclaim 1 wherein the modified starch exhibits a Brookfield viscosity ofat least about 1 cps.
 6. The desiccant composition of claim 1 whereinthe modified starch is an oxidized starch.
 7. The desiccant compositionof claim 1 wherein the modified starch is an enzyme-converted starch. 8.The desiccant composition of claim 1 wherein the modified starchcomprises at least one functional group selected from the groupconsisting of hydroxyl, carbonyl, amido and amino groups.
 9. Thedesiccant composition of claim 1 wherein the modified starch is modifiedby a process selected from the group consisting of cross linking,substitution and granulation.
 10. The desiccant composition of claim 1wherein the modified starch is an oxidized, enzyme-converted starch. 11.A desiccant composition comprising calcium chloride and a modifiedstarch, wherein the calcium chloride comprises at least about 5 to about95 percent of the composition by weight and the modified starch fromabout 5 to about 95 percent of the composition, wherein the modifiedstarch is selected from the group consisting of oxidized starches,enzyme-converted starches or hydroxyethylated starches.
 12. A desiccantcontainer comprising a desiccant composition secured within a watervapor permeable film product, wherein the desiccant composition calciumchloride and a modified starch, wherein the calcium chloride comprisesat least about 5 to 95 percent of the composition by weight and themodified starch from about 5 to 95 percent of the composition by weight.13. The desiccant container of claim 12 wherein the calcium chloridecomprises from about 20 to about 95 percent of the desiccant compositionby weight and the modified starch from about 5 to about 80 percent ofthe composition by weight.
 14. The desiccant container of claim 12wherein the calcium chloride comprises from about 50 to about 80 percentof the desiccant composition by weight and the modified starch fromabout 20 to about 50 percent of the composition by weight.
 15. Thedesiccant container of claim 12 wherein the modified starch is amodified corn starch.
 16. The desiccant container of claim 12 whereinthe modified starch exhibits a Brookfield viscosity of at least about 1cps.